Return a list of 3-element tuples, each describing a particular type of
module. Each triple has the form (suffix,mode,type), where suffix is
a string to be appended to the module name to form the filename to search
for, mode is the mode string to pass to the built-in open() function
to open the file (this can be 'r' for text files or 'rb' for binary
files), and type is the file type, which has one of the values
PY_SOURCE, PY_COMPILED, or C_EXTENSION, described
below.

Try to find the module name. If path is omitted or None, the list of
directory names given by sys.path is searched, but first a few special
places are searched: the function tries to find a built-in module with the
given name (C_BUILTIN), then a frozen module (PY_FROZEN),
and on some systems some other places are looked in as well (on Windows, it
looks in the registry which may point to a specific file).

Otherwise, path must be a list of directory names; each directory is
searched for files with any of the suffixes returned by get_suffixes()
above. Invalid names in the list are silently ignored (but all list items
must be strings).

If search is successful, the return value is a 3-element tuple (file,pathname,description):

file is an open file object positioned at the beginning, pathname
is the pathname of the file found, and description is a 3-element tuple as
contained in the list returned by get_suffixes() describing the kind of
module found.

If the module does not live in a file, the returned file is None,
pathname is the empty string, and the description tuple contains empty
strings for its suffix and mode; the module type is indicated as given in
parentheses above. If the search is unsuccessful, ImportError is
raised. Other exceptions indicate problems with the arguments or
environment.

If the module is a package, file is None, pathname is the package
path and the last item in the description tuple is PKG_DIRECTORY.

This function does not handle hierarchical module names (names containing
dots). In order to find P.M, that is, submodule M of package P, use
find_module() and load_module() to find and load package P, and
then use find_module() with the path argument set to P.__path__.
When P itself has a dotted name, apply this recipe recursively.

Load a module that was previously found by find_module() (or by an
otherwise conducted search yielding compatible results). This function does
more than importing the module: if the module was already imported, it will
reload the module! The name argument indicates the full
module name (including the package name, if this is a submodule of a
package). The file argument is an open file, and pathname is the
corresponding file name; these can be None and '', respectively, when
the module is a package or not being loaded from a file. The description
argument is a tuple, as would be returned by get_suffixes(), describing
what kind of module must be loaded.

If the load is successful, the return value is the module object; otherwise,
an exception (usually ImportError) is raised.

Important: the caller is responsible for closing the file argument, if
it was not None, even when an exception is raised. This is best done
using a try … finally statement.

Reload a previously imported module. The argument must be a module object, so
it must have been successfully imported before. This is useful if you have
edited the module source file using an external editor and want to try out the
new version without leaving the Python interpreter. The return value is the
module object (the same as the module argument).

When reload(module) is executed:

Python modules’ code is recompiled and the module-level code reexecuted,
defining a new set of objects which are bound to names in the module’s
dictionary. The init function of extension modules is not called a second
time.

As with all other objects in Python the old objects are only reclaimed after
their reference counts drop to zero.

The names in the module namespace are updated to point to any new or changed
objects.

Other references to the old objects (such as names external to the module) are
not rebound to refer to the new objects and must be updated in each namespace
where they occur if that is desired.

There are a number of other caveats:

When a module is reloaded, its dictionary (containing the module’s global
variables) is retained. Redefinitions of names will override the old
definitions, so this is generally not a problem. If the new version of a module
does not define a name that was defined by the old version, the old definition
remains. This feature can be used to the module’s advantage if it maintains a
global table or cache of objects — with a try statement it can test
for the table’s presence and skip its initialization if desired:

try:cacheexceptNameError:cache={}

It is legal though generally not very useful to reload built-in or dynamically
loaded modules, except for sys, __main__ and builtins.
In many cases, however, extension modules are not designed to be initialized
more than once, and may fail in arbitrary ways when reloaded.

If a module imports objects from another module using from …
import …, calling reload() for the other module does not
redefine the objects imported from it — one way around this is to re-execute
the from statement, another is to use import and qualified
names (module.*name*) instead.

If a module instantiates instances of a class, reloading the module that defines
the class does not affect the method definitions of the instances — they
continue to use the old class definition. The same is true for derived classes.

Changed in version 3.3: Relies on both __name__ and __loader__ being defined on the module
being reloaded instead of just __name__.

Return the PEP 3147 path to the byte-compiled file associated with the
source path. For example, if path is /foo/bar/baz.py the return
value would be /foo/bar/__pycache__/baz.cpython-32.pyc for Python 3.2.
The cpython-32 string comes from the current magic tag (see
get_tag(); if sys.implementation.cache_tag is not defined then
NotImplementedError will be raised). By passing in True or
False for debug_override you can override the system’s value for
__debug__, leading to optimized bytecode.

path need not exist.

Changed in version 3.3: If sys.implementation.cache_tag is None, then
NotImplementedError is raised.

Given the path to a PEP 3147 file name, return the associated source code
file path. For example, if path is
/foo/bar/__pycache__/baz.cpython-32.pyc the returned path would be
/foo/bar/baz.py. path need not exist, however if it does not conform
to PEP 3147 format, a ValueError is raised. If
sys.implementation.cache_tag is not defined,
NotImplementedError is raised.

Changed in version 3.3: Raise NotImplementedError when
sys.implementation.cache_tag is not defined.

Return the PEP 3147 magic tag string matching this version of Python’s
magic number, as returned by get_magic().

Deprecated since version 3.4: Use sys.implementation.cache_tag directly starting
in Python 3.3.

The following functions help interact with the import system’s internal
locking mechanism. Locking semantics of imports are an implementation
detail which may vary from release to release. However, Python ensures
that circular imports work without any deadlocks.

Return True if the global import lock is currently held, else
False. On platforms without threads, always return False.

On platforms with threads, a thread executing an import first holds a
global import lock, then sets up a per-module lock for the rest of the
import. This blocks other threads from importing the same module until
the original import completes, preventing other threads from seeing
incomplete module objects constructed by the original thread. An
exception is made for circular imports, which by construction have to
expose an incomplete module object at some point.

Changed in version 3.3: The locking scheme has changed to per-module locks for
the most part. A global import lock is kept for some critical tasks,
such as initializing the per-module locks.

The NullImporter type is a PEP 302 import hook that handles
non-directory path strings by failing to find any modules. Calling this type
with an existing directory or empty string raises ImportError.
Otherwise, a NullImporter instance is returned.

The following function emulates what was the standard import statement up to
Python 1.4 (no hierarchical module names). (This implementation wouldn’t work
in that version, since find_module() has been extended and
load_module() has been added in 1.4.)

importimpimportsysdef__import__(name,globals=None,locals=None,fromlist=None):# Fast path: see if the module has already been imported.try:returnsys.modules[name]exceptKeyError:pass# If any of the following calls raises an exception,# there's a problem we can't handle -- let the caller handle it.fp,pathname,description=imp.find_module(name)try:returnimp.load_module(name,fp,pathname,description)finally:# Since we may exit via an exception, close fp explicitly.iffp:fp.close()